In some of the current motor vehicles that are e quipped with various onboard devices, the device control units for such onboard devices are enabled to communicate with one another via a network such as a CAN (controlled area network). The CAN may include a multiplex communication line serving as a common bus via which a plurality of nodes are connected to a recording device. The recording device collects data from the device control units, and may be detachably connected to the common bus via a connector so that the data collected by the recording device may be used for analyzing the behavior and the operating condition of the vehicle and diagnosing the failure of the vehicle (See patent document 1, for instance.).